1. Field of the Invention
The present invention relates to a zoom lens that can be used for an imaging optical system using a solid state imaging device and can be made compact and light at low cost.
2. Description of the Related Art
In general, zoom lenses used in still cameras or video cameras should have excellent optical performance, a high zoom ratio, and a compact design. Moreover, with the widespread use of electronic equipment such as portable information terminals, e.g., personal digital assistants (PDAs) or mobile terminals, digital cameras or digital video units are increasingly installed in such electronic equipment. As a result, cameras should be more compact. Solid state imaging devices, such as charge coupled devices (CCD) or complimentary metal-oxide semiconductors (CMOSs), used for electronic still cameras or video cameras, should also be compact, light, and inexpensive.
FIG. 1 is a cross-sectional view illustrating an optical configuration of a conventional zoom lens disclosed in U.S. Pat. No. 6,804,064 B2. Referring to FIG. 1, the conventional zoom lens includes a first lens group L1 having a first lens 1, a second lens 2, and a third lens 3; a second lens group L2 having a fourth lens 4, a fifth lens 5, a sixth lens 6; and a seventh lens 7; and a third lens group L3 having an eighth lens 8. The second lens group L2 consists of the fourth lens 4 having a positive refractive power, the sixth lens 6 having a positive refractive power and a meniscus shape convex toward an object, and the seventh lens 7 that has a positive refractive power, which are arranged sequentially from the object.
The first through third lens groups L1 through L3 of the conventional zoom lens are moved during zooming. When zooming is performed from a wide angle position to a telephoto position, the second lens group L2 is moved a great distance, thereby increasing the size of the zoom lens optical system and requiring a large receiving space. Also, since the doublet of the second lens group L2, which is used for chromatic aberration correction, is too thick, the size of the zoom lens optical system is increased even further.
Japanese Patent Laid-Open Publication No. 2003-050352 discloses a zoom lens in which a first object-side lens of a second lens group is a plastic aspheric lens. In this case, it is difficult to correct spherical aberration during zooming of the optical system and achieve a zoom ratio of 2× or more.